He said an effort to drill a relief well designed to seal the leaking well is ahead of schedule and could reach the damaged well pipe in two to three weeks.

But Allen was reluctant to predict that oil company BP would be able to permanently seal the well before the original August prediction.

Allen said efforts are continuing to increase the amount of oil contained from the leaking well. He said the current containment system is expected to reach its maximum level of about 53,000 barrels a day by the end of June.

Allen said by July 1, a decision will have to be made on whether the current containment system should be left in place until the relief well is finished, or if it should be changed to a system with higher capacity and better resistance to hurricanes.

He said the new system, if successful, could increase containment capacity to as much as 60,000 barrels a day, but would require installing a new cap on the well riser, which does involve risks.

On Thursday, BP Chief Executive Officer Tony Hayward was subjected to intense questioning about BP procedures, as he testified before a U.S. House of Representatives subcommittee.

Hayward told the panel he feels a "great deal of responsibility" for the massive oil spill, but it is too early to tell what caused it.

Lawmakers accused the company of taking dangerous shortcuts to save time and money.

Hayward repeatedly said he was not involved in the decision-making process, or that he was waiting for the results of BP's own investigation into the disaster, which began April 20 when an oil rig off the coast of Louisiana exploded.

Republican Joe Barton apologized to Hayward for what the lawmaker called a "$20-billion shakedown" by the White House. Barton later retracted that statement. He had been referring to the $20-billion compensation fund that was announced Wednesday after BP officials met with U.S. President Barack Obama at the White House.

The oil rig explosion killed 11 workers. President Obama has described the spill as the worst environmental disaster the country has ever faced. In his testimony, Hayward pledged BP will cover all clean-up costs and legitimate claims for losses and damages.